vaadin superdevmode can't find custom widget classes

I'm trying to debug a Vaadin custom widgetset using superdevmode. In "normal" mode the custom widget shows up correctly in the browser. When using superdevmode though, it shows the following text instead of the custom widget:

Widgetset xxx does not contain implementation for yyy

Tried all the usual things such as recompile from command line, restart superdevmode server, to no avail.

The weird thing is that the class in the error message (yyy above) is a server side class, used in the client side code only in @Connect(yyy.class), in the client side Connector. Obviously compiled widgetsets do not contain server side classes. So why would it complain about this class?

Also the fact that it works in normal mode makes me wonder what can be wrong. Many similar questions throughout the forums are unanswered. Any help would be appreciated.

Using Vaadin 7.6.6

Contents of widgetset.gwt.xml:

<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE module PUBLIC "-//Google Inc.//DTD Google Web Toolkit 2.5.1//EN"
        "http://google-web-toolkit.googlecode.com/svn/tags/2.5.1/distro-source/core/src/gwt-module.dtd">
<module>
    <set-configuration-property name="devModeRedirectEnabled" value="true" />
    <add-linker name="xsiframe" />

    <inherits name="com.vaadin.DefaultWidgetSet" />
    <inherits name="..." />

    <source path='client' />
    <source path='shared' />

    <stylesheet src="resetbuttonfortextfield/styles.css" />
</module>

Solved it eventually by adding -src ${project_loc}/src/main/java to my superdevmode run configuration. Beats me why it wasn't able to figure that for itself.