Even educated people can now be heard saying "tą sprawę", "weź tą rękę", "widzę tą koleżankę" in the accusative singular -- politicians, cultural celebrities, people with PhDs..,with the possible exception of Polish philologians. I beleive "tą" is still considered wrong, but when nearly everybody is using it, the grammatcially correct form will probably soon become a relic and oddity. The pressure towards uniformity in language is a stong force indeed!
Not so long ago (19th century), all inflected personal possessive adjectives (mój, swój, twój, nasz, wasz) took the -ę ending in the feminine singular: Kocham swoję żonę; Rozumiem waszę tragedię... but that did not make it into the 20th century, and the -ę ending has survived only in the fem. accsuative singular of the demonstrative pronoun "ta". How much longer? Which form do you use normally? Does it differ in speech and writing?
The more frequently used the word then the slower it evolves. Apparently that's the general rule of thumb. I guess that is why tę has not fully evolved into tą yet like the other forms did and we get the situation now where what is technically correct sounds odd.
It makes life harder for me as a non-native speaker to know which form to go with..
One of the criteria of correctness (as taught in Polish high schools) is the frequency of use. This is not the only criterion though so alone, it may not be sufficient. Still, "TĘ" is, by some Polish linguists, considered hypercorrectness (negative term) when used in speech, but correct in writing.
IINM about 20 years ago tą kobietę was considered incorrect while speaking. For at least 10 years it's been considered okay in everyday speech but not approved of in very formal speech or any writing. I think within ten or 20 years it will be approved for written use to alongside tę which will linger on in extremely formal usage.
Also IINM the old instrumental plural ending -y was required in writing a long time after it was displaced by -(a)mi in speech.
Well, "tą książkę" is hard to say anyway. People are strange... ;) Generally, we use "tą" when talking about Narzędnik "idę z tą panią", "idę z tą książką". When we go to Dopełniacz, it should be "tę".
I think the different thing is how educated people talk. Cause education in geography doesn't mean a linguistic consciousness. And as I remember my high school English lessons with native speakers, it doesn't concern only Polish people ;)
I think people don't even understand this, cause they prefer hiring people with English degree to translate from English to Polish (than people with degree in Polish). And in this kind of translation the perfect Polish language consciousness is needed which is NOT equivalent to 'mother tongue'.
By the way, I'd like to take the opportunity to ask if the biernik declension for "tamten" (feminine singular) has the same ending: "tamtę" (instead of "tamtą" you would normally expect there). Thanks.