Pix-Art Messenger is an XMPP client which will connect to almost any XMPP server. Pix-Art Messenger will never upload data to the developer automatically. The only execption to this rule is data collected after a crash, but you will be aksed to send the information. This data will be sent via your own XMPP account but never automatically without your consent.
Pix-Art Messenger or its developers don't have control over the data you send through the messenger. However the following data might get uploaded to your XMPP provider:
Using the pix-art.de XMPP provider is optional. You can choose any other XMPP provider.