Thanks for your thoughts, Danny.
The first thing you'll need to share with us to receive good advice is what wallet software (and what version of that software) you are using.
In your post you state that you used Bitcoin-QT in January, but I assume you either used a different wallet this time, or you changed some settings on your Bitcoin-Qt wallet because Bitcoin-Qt doesn't re-use the same bitcoin address when you have the default settings.
0) I don't need to delete the TAs from wallet(-history), but from unconfirmed-TA-bitcoin-network-(nodes-)pool ! (I have older usable back-up wallets).
1) Always I use bitcoin-qt 0.8.6.0 since the last years.
2) You are wrong. Bitcoin-Qt 0.8.6.0 (and also older version I used) reuse the same bitcoin address often -- as I can simply state from own expierience.
It is a pity that you can not see the set of in-use-addresses and moreover control from which addresses coins should be used/sent for a new TA. :-/
3) Meanwhile both Tas are deleted from the unconfirmed TA-Pool listed at blockchain.info. It happens during I wrote my first message about 3,5 hours ago (which sadly got lost due to user-error on handling this web-posting-software while reviewing). Thus I know it was more than 48 hours listed but less than 49 hours. The second seems to be deleted in the same short time interval. Thus I assume someone (at blockchain.info?) removed both Tas manually after reading my post here.
Thank you.
Regards
achim