[Typo3-dev] My extended extension (ux_ttproducts) annihilated by installing another extension

[Tomasz M]

Dear Folks,

I've extended tt_products. In accordance with the
documentation ("Inside Typo3" etc) I put my files in
typo3conf/ext/tt_products (class ux_tx_ttproducts in file 
pi/class.ux_ttproducts.php plus a handle script for debit cards and 
templates), activated the class with an appropriate switch in 
localconf.php, added $TCA for my new tables in 
typo3conf/extTables.php - and everything worked excellent...

...until the admin installed another extension. Then
- in the BE all content records containing the shop plugin started to
show "Current value not available (5)" or something like that,
- all content elements containing shop plugin disappeared from the 
site; that is, they are there, in the FE editor I can see their 
pencil icons and I can edit them, but no content is generated

I tried to reproduce the previous state and work out some
countermeasures.
I found out that at the moment of installing the next plugin 
(regardless of its name)
-  the tt_products configuration was removed from 
typo3conf/temp_CACHED_****ext_tables.php (lines/sections ##EXTENSION, 
##FILE, $_EXTKEY, $TCA["tt_products"],
t3lib_extMgm::addPlugin / allowTableOnStandardPages /
addToInsertRecords, $TBE_MODULES_EXT...)
- in the template analyzer I could no longer see anythng regarding 
plugin.tt_products apart from a few lines from the TS template 
(nothing from the config files ext_typoscript....txt)
- if all files* from typo3/ext/tt_products/ were copied to
typo3conf/ext/tt_products before installing the next extension, the
shop plugin appeared correctly in the BE, but nothing showed up on
the web site (
[* normally I put no files into /typo3conf/ext/tt_products - there is
just the pi/ directory; ext_typoscript_(constants|setup).txt, 
tables.php, tca.php etc reside
in their original directory typo3/ext/tt_products ]

Was this my mistake or a Typo3 bug? And more important - can anyone
tell me, how to repair my site?

much health to you all

Tomasz M