Mouse click not setting ins point in 8.7.2

Every now and then it happens.
I click somewhere in a paragraph, select a letter by dragging the mouse and type
a couple characters.
Well, the new characters appear where the insertion point was before clicking,
in another line or in other paragraph.
At first it looks like an error of self. But after several times it morphs into
a bug. It's not a mouse failure: the text to be replaces IS selected.
I'm sorry I had no time to write instructions to provoke the error. Is aomebody
else experiencing this?
--
Juan Lanus
TECNOSOL
Argentina