After all I am nearly sure, that the Ungarische Fantasie op.45 is a composition from Franz Lehar jr. I would like to collect the arguments.
1. Lehar jr. feels as Hungarian and speaks this language as native language, Lehar sr. is born
in eastern “Sudetenland” and speaks nearly no Hungarian. Lehar jr,. was violinist, whereas
Lehar sr. was a horn player. So it´s much more likely for the son to compose a Ungarische
Fantasie for violin as solo instrument.
2. The composition was first mentioned in “Verzeichnis der 1897 erschienenen Musikalien“.
In this volume is one composition of Lehar jr. and there are five compositions of Lehar (without Jr. or sr.) The Ungarische Fantasie is the first one of these.
The compositions 4. and the 5. are definitely from Lehar jr. There is no reason, why the other 3 should not be from Lehar jr.
3. In the “Handbuch der musikalischen Werke 1900” we find 20 entries for Lehar jun.,
8 entries for Lehar sen, and no entry for Lehar without an addition. So it seems, the
Editor wants to decide, whether a composition is from jr. or sr. All the 5 entries of the
“Verzeichnis” under Lehar occurs now under Lehar sen. The reason probably is the
simple, but false conclusion: What does not have the additional jr. must be sr.
4. In the “Handbuch der musikalischen Werke 1906” only Lehar appears, there is no longer
a discrimination between sr. and jr. It seems, that one has realized, that all the former mentioned compositions are from Lehar jr.
Nowadays the only trace of Lehar sr. as composer seems to be three marches on a cd of marches from Lehar sr and Lehar jr.
5. In 1935 a new edition of op. 45 appears under the name of the famous Franz Lehar.
If this would be an incorrect attribution, Franz Lehar would have probably filed a protest.
6. There is a “Werkeverzeichnis” for Lehar. The Ungarische Fantasie is NV 151.
So i would propose to delete the page Franz Lehar sr. and to shift the compostion to Franz Lehar.