Why doesn't διαστρώσαντα get hopperized?

[ἑκηβόλος]

Is there a morphological irregularity in διαστρώσαντα? Perseus doesn't recognise it - diastrw/santa

It is found in Lucian's Dialogi deorum 24, 1.

διαστρώσαντα τὴν κλισίαν

Within the discourse it is aorist and within the syntax it is an accusative singular masculine participle of διαστρώννυμι, as εὐθετίσαντα is, so no surprises there.

Is it an irregular form in some way?

[bedwere]

Smyth has

στρών-νυ_μι (στρω-) spread out: ὑπο-στρώσω, ἔστρωσα Tragic, Hdt., ἔστρωμαι, στρωτός poetic. Cp. στόρνυ_μι. (IV.) (Attic) LSJ

[ἑκηβόλος]

Looking at the LSJ entry for στόρνυμι, which that Smyth reference hyper-links to, the verb shows a great deal of conjugational (morphological) variety.

[jeidsath]

No variations of στόρνυμι or compounds show up in Perseus search. It's a Morpheus bug.

[ἑκηβόλος]

No variations of στόρνυμι or compounds show up in Perseus search. It's a Morpheus bug.

Agent Smith seems to have gained access to the Aretaeus the Cappadocian program too.