CalDAV/CardDAV sync error

I sync my contacts an my calendar to a self hosted CardDAV/CalDAV server (baikal). However, every time it syncs, I get the error “Invalid URI: The Uri string is too long.”

As far as I see, all changes are saved and synced to my mobile, however getting the error is annoying and I could not double check every entry.

Is there any way to find out where it might be stuck, or is this even considered a bug?

The complete content of the "Protocol" tab in the sync window is:
16:33:57 [CalDAV / CardDAV]  Die Elemente werde hochgeladen: Fertig
16:33:57   System.UriFormatException: Invalid URI: The Uri string is too long.
16:33:57    at System.Uri.CreateThis(String uri, Boolean dontEscape, UriKind uriKind)
16:33:57    at System.Uri..ctor(String uriString)
16:33:57    at MailClient.Contact.ContactConvert.StoreImageToProperty(Card card, String propertyName, Byte[] image, Version version, Boolean forceJpeg)
16:33:57    at MailClient.Contact.ContactConvert.UpdateCardFromContact(Card& card, IContact contact, Version version, ContactConvertOptions options)
16:33:57    at MailClient.Storage.Application.Contact.ContactItem.GetCard(Version version)
16:33:57    at MailClient.Protocols.CalDav.Synchronizer.ContactItemSynchronizer.GetPayload(Folder folder, IContactRepositoryItem item)
16:33:57    at MailClient.Protocols.CalDav.Synchronizer.ContactItemSynchronizer.GetPayload(Folder folder, IContactRepositoryItem item, String& contentType)
16:33:57    at MailClient.Protocols.CalDav.Synchronizer.UploadCommand`1.DoUpload(Uri selectPath, TStorageItem item, Boolean overwrite)
16:33:57    at MailClient.Protocols.CalDav.Synchronizer.UploadCommand`1.Execute(WorkerStatus status)
16:33:57    at MailClient.Commands.Command.Process(WorkerStatus status)