Dropping parts of the root.

Hi, folks!

We all know about agglutinating and inflecting languages where morphemes are
added to a root to change its meaning or function in the sentence. I was
wondering: are there instead natlangs marking a morphologic feature deleting
a part of the root? The only one I can think about is French. From the
infinitive _rendre_ /R6~dR/ we get _je rendais_ /ZR6~'de/ in the imperfect,
but _je rends_ /ZR6~/ in the present tense, dropping /d/ because of
historical trivia; or the way it marks masculine adjectives, that is often
dropping the femminine last consonant - we discussed it some months ago,
remember?

In Draseléq (P. Flores' best conlang) the verb shows a consonant (Extended
Stem Consonant) in some inflected forms, while in others it is dropped:

drasten 'to cross'
dras 'he/she/it crosses'
drasut 'we cross'
draster 'you (pl) cross'
drasek 'they cross'

Are there natlangs showing such a strange arrangement? And how did they
develop it?

Thanks in advance,

Luca